RESEARCH SUMMARY: Adsorption of surfactants from aqueous solution is an important but complex phenomenon due to the influence of factors including surfactant structure (functional groups, chain length, branching), solid mineralogy and morphological heterogeneity and solution properties. Absorption (loss) of surfactants is investigated here by studying their interactions with minerals, dissolved mineral species, polymers, oils and alcohols. In order to understand the absorption phenomenon, in the previous grant, other key properties such as zeta potential, wettability, CMC, mineral dissolution and surfactant chromatographic separation were monitored. It was shown that when soluble and semisoluble solids are present, there will be not only alterations of the solids due to surface precipitaiton but also depletion of surfactants due to bulk precipitation. A major process responsible for surfactant loss has been identified to be, in addition to electrostatic and hemimicellar absorption, surfactant precipitation particularly in solutions containing metal ions. It appears now that surfactants can be suitably modified to tolerate such hostile environments. Particular emphasis is being placed on ethoxylated surfactants since they can be manipulated to yield desired interfacial tension and salt tolerance. The PI has already obtained total inhibition of precipitaton with certain ethoxylated sulfonates in gypsum containing substrates which are normally very hostile to sulfonates. The role of structural modifications such as ethoxylation is not fully understood, but can be studied using a combination of techniques. It is the aim of the proposed work to investigate (using absorption, electrokinetic, chromatographic and spectroscopic techniques). The mechanisms by which structural modifications affect absorption/precipitation and to identify the reasons for the selective/preferential absorption or synergism observed in mixed systems of the above surfactants. UNIQUENESS AND INNOVATION: In contrast to other work on absorption, this research includes also the effects on absorption of dissolution of the solid and interaction of the dissolved species with the surfactant leading to complexation and even precipitation. Solids invariably dissolve and the dissolved species often govern the entire absorption (abstraction) behavior and yet these effects have been ignored in the past. In this research, the effect of dissolved species is being quantitatively determined and the absorption/desorption phenomenon and hysteresis phenomenon explained.
